This invention relates generally to a Monitoring and Diagnostics system and, more particularly, to a communication method, in particular to a communication method for communicating between a Programmable Logic Controller and a central unit.
Monitoring and Diagnostics systems (M&D systems) are commonly used whenever apparatuses need to be monitored. Such systems are particularly useful if a plurality of apparatuses that are spread over an extended area or that are otherwise difficult or inconvenient to access need to be monitored (Remote Monitoring and Diagnostics systems, or RM&D systems). For example, given the geographical spread of wind turbines, it is usually not feasible for an operator to be at a given wind turbine. Further examples include solar panels, medical apparatuses, elevators, locomotives, traffic control systems, and the like. M&D systems include sensors in the apparatuses that indicate faults and communication lines to transmit the sensor signals to a central location, where a human operator is able to analyze the signals and take appropriate actions.
One issue regarding M&D systems is the response time, i.e. the time span between the fault event and the initiation of appropriate actions. It is desired to have short response times, because, for example, apparatus faults can lead to apparatus unavailability, further damage to the apparatus, or to an increased risk (e.g. in the case of medical equipment or of traffic control systems).
In M&D systems, the response time depends on the availability of a human operator. For example, if a wind turbine connected to a M&D system faults, it usually stops its operation until an operator is able to analyze its condition, to establish that a reset of the turbine is feasible and to perform the reset, During that period, the turbine is unavailable and does not produce energy. To improve the response time, an operator needs to be available when the turbine faults. However, permanent operator availability is costly, and is still not a guarantee for a short response time, e.g. in the case of simultaneous faults in multiple apparatuses.
Communication methods between Programmable Logic Controllers and other systems have been using, in most cases, static protocols, i.e. protocols, in which data items are transmitted according to a predetermined structure. These protocols are hard to extend. For example, the positions at which information could be found and also the type and length of each data point are usually the same and have no dynamic aspect.
Protocols allowing for a more flexible data transmission from or to Programmable Logic Controllers are also known, for example the protocols according to the norms IEC 60870-5-104 and JEC 61850. These protocols allow transmitting data along with information regarding the structure of the transmitted data. However, both the data and the information are transmitted in the same channel, whereby the performance of the protocol is degraded. Also, a clear distinction between raw data and information can be desirable e.g. for optional compatibility with respect to other static protocols.